A solid color coating composition containing an aminoplast as a curing agent has been conventionally widely known. However, in the case of a coating composition containing as a curing agent only an aminoplast, a crosslinked portion of a coated film has poor acid resistance, and the coated film is damaged by acid rain which has recently become a serious problem.
The present inventors have already suggested a curable resin composition comprising a polymer having a specific halfester group and a polymer having a hydroxyl group and an epoxy group, in Japanese Patent Laid-Open Publication No. Hei 3-287650. This composition is excellent in acid resistance and is not damaged by acid rain, since it uses an acid anhydride curing system. However, the coating system suggested by these inventors is basically designed to obtain a clear coating. Therefore, a solid color coating composition containing a pigment has not been investigated.
In the case of solid color, excellent appearance, high mar resistance and the like are required as well as the above-described acid resistance. Further, it is important that the coating composition is high solid. On the other hand, to obtain high mar resistance together with the acid resistance, it is indispensable to make a crosslinked coated film having high density. As a result, a problem occurs that stress strain is concentrated in the interface of a coated film in curing with thermosetting, and consequently adhesion to an undercoat becomes poor.
The present invention has been made to solve the above-described conventional problems, and the object thereof is to provide a solid color coating composition which suffices scratch resistance, acid resistance, storage stability and excellent appearance.